1. Technical Field
The present invention relates generally to material compaction, and more particularly, to a member, screed and method for realigning material and compacting.
2. Related Art
During material compaction in, for example, an asphalt paving environment, it is always advantageous to attain a high compaction rate in as little time as possible. A high compaction rate insures pavement longevity and thus reduces costly repairs. Similarly, speed of attaining a high compaction rate reduces paving costs.
A conventional approach to paving is shown in FIGS. 1 and 2. As shown in FIG. 1, an initial step includes applying a screed 10 to a paving material 12 that is placed in front of screed 10, which moves in a direction of travel DT. Paving material 12 may be, for example, e.g., asphalt. Conventional screeds normally include a receiving member 14 and a horizontal member 16 coupled to receiving member 14 by a nose 18. Screed 10 controls the depth of a raw paving material mat 20 that exits therefrom, provides a partial compaction of paving material 12 at nose 18, and smoothes paving material 12 with some compaction as it passes under horizontal member 16. The primary compaction zone is at nose 18 of screed 10 as shown in FIG. 1.
A conventional second step, as shown in FIG. 2, includes rolling raw paving material mat 20 with a roller 22 to generate a rolled mat 24. FIG. 2 also shows a side-by-side comparison of  paving material aggregate 30A exiting a screed and rolled paving material aggregate 30B. As rolling occurs, compaction of paving material 12A occurs via the weight of roller 22 and gravity in a vertical direction causing voids areas 32 to be filled with the aggregate 30B and asphalt binders 34. Prior to vertical compaction, however, roller 22 also moves paving material 12A in front of roller 22 in a substantially horizontal direction of travel that causes a waveform 36, thus moving aggregate 30A in a substantially horizontal direction and aiding realignment of aggregate 30B into a more compacted paving material 12B. This two-directional motion, substantially horizontal and vertical, increases the density of the paving material.
A shortcoming of the above approach is that target compaction rates, e.g., 94–96%, require many rolling passes, which reduces productivity and increases costs. Unfortunately, with the current art, further rolling does not guarantee reaching a target or uniform compaction rate.
One reason for this situation is that aggregate may still be vertically aligned because prior compaction by the screed and roller does not realign aggregate in other than the vertical direction and the one substantially horizontal direction of travel caused by waveform 36. For example, referring to FIG. 2, vertically overlapping aggregate particles 40A, 42A, one or more of which includes a substantial dimension in the direction of travel, may continue to vertically overlap after an initial rolling pass —see aggregate particles 40B, 42B. Where one or more of aggregate particles 40A, 42A includes a relatively minimal lateral dimension, movement in a lateral horizontal direction may eliminate the overlap and allow for greater compaction. Unfortunately, no conventional approaches address this possibility. Additional rolling provides minimal horizontal realignment in a direction of travel because the size of waveform 36 diminishes with higher density. Accordingly, additional rolling may never provide enough horizontal realignment to overcome the  overlap, and may result in undesirable aggregate fracture. In some cases, vibratory screeds are used to vibrate in a vertical direction in the attempt to provide additional compaction. However, the compaction improvement provided by these screeds is also limited because the aggregate is not moved to re-align. Thus the aggregate would need to fracture to cause additional improved compaction.
In view of the foregoing, there is a need in the art for a way to provide an additional mechanism for paving material aggregate realignment so further compaction can be attained.